1. Field of the Invention
The present invention relates to a method and an apparatus for making desired copies from a plurality of video programs stored in a main server and transmitting the copies of the video programs from a cache server.
2. Description of Related Art
As the transmission of data such as over CATV (cable television) systems has been realized in multiple channels, the demand for recording or playing back two or more video/audio data in one single video/audio data recorder/player apparatus and also, simultaneous recording and playing back of the video/audio data is increased. For satisfying the demand, an advanced apparatus, called a video server (or an AV (video and/or audio) server), is recently introduced for recording and playing back the video/audio data on a random access recording medium such as a hard disk.
It is commonly desired for increasing the quality of reproduced images and sounds that such a video server as employed in a broadcasting station has a large storage capacity for storage of long lasting data and is compatible to a higher rate of data transmission. For the purpose, the data recorder/player apparatus is provided with a number of hard disks (abbreviated to HDs) which can save a large quantity of video/audio data and allow parallel processing of the same. In addition to improvement of the data transmission rate and increase of the storage capacity, an attempt is made in which parity data is saved which can be used for maintaining the operational reliability when any of the HDs has a fault. Even if the number of channels determined by the requirements at a broadcasting station, e.g. of programs and transmission modes, is varied, that type of the video server permits simultaneous transmission over the channels of a material data which comprises multiple video and audio signals and are saved in a discrete manner or playing back of the same at intervals of a time of delay on the channels and can act as a multi-channel video server applicable to a wide range of equipment including a VOD (video-on-demand) system and an NVOD (near video-on-demand) system.
In practice, it is known that video programs to be transmitted for broadcasting are stored in a video server and when requested, desired ones of them are temporarily saved in another video server before distributed to each subscriber. It is noted that the former video server for storage of all the video programs is termed as a main server and the latter for temporal storage of desired video programs called as a cache server. An apparatus for, upon request, automatically transferring (or copying) a desired one of the video programs from the main server to the cache server which in turn distributes the video program to clients is known as an automatic copying system.
In such an automatic copying system, when not saving a video program desired for transmission to a home client, the cache server can receive a copy of the desired video program from the main server and deliver it to the home client.
In common, when the cache server carries no programs, the video programs are copied in the order of transmission from the cache server.
If the order of transmission from cache server to clients is changed, the order of copying the video programs has to be changed. Otherwise, some of the video programs to be transmitted are not saved in the cache server and fail to be distributed to the clients.
Also, when the insertion of another video program to be copied and transmitted according to transmission change is made, it interrupts copying of the current video program and thus the action of the main server, the cache server, and their relevant controllers hence declining the efficiency of data processing.
The present invention is directed in view of the foregoing drawbacks and its object is to provide a method of image data transmission in which when the transmission of programs is changed and a desired program has to be copied from the main server to the cache server, the copying is carried out in a modified order of priority so as to increase the efficiency.
According to the present invention, a method of transmitting programs, each comprising a group of data, which are stored in a first saving means and copied to a second saving means before distributed out from the second saving means, comprising the steps of: saving a database file which includes data of the programs saved in the second saving means, a playback file which includes data of transmission of the programs saved in the second saving means, and a copy file indicative of programs in the order of transmission which are listed in the playback file but not saved in the database file; transferring to the first saving means a first copy demand for copying the programs specified by the copy file; copying the programs from the first saving means to the second saving means in response to the first copy demand; when the playback file is changed, examining whether the video program specified by the copy file is to be transmitted urgently or not; when a program added and/or modified is to be transmitted urgently and earlier than the current program being copied to the second saving means, transferring to the first saving means a second copy demand for interrupting the copying of the current program and copying the program added and/or modified at priority; and copying the program added and/or modified from the first saving means to the second saving means in response to the second copy demand.